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authorColin Watson <cjwatson@debian.org>2005-03-10 00:24:57 +0000
committerColin Watson <cjwatson@debian.org>2005-03-10 00:24:57 +0000
commit5d05471f6657646d1d6500c7c43134462c407ee6 (patch)
treec142ff8a5b1fcb1c671ba8c6f023746191124d39 /ssh_config.0
parent485bab886137bbf8b7ec8df82bd66dc6e5654371 (diff)
parentebd2ce335af5861020c79fddb1ae35c03bf036cf (diff)
Import OpenSSH 4.0p1.
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1SSH_CONFIG(5) OpenBSD Programmer's Manual SSH_CONFIG(5)
2
3NAME
4 ssh_config - OpenSSH SSH client configuration files
5
6SYNOPSIS
7 $HOME/.ssh/config
8 /etc/ssh/ssh_config
9
10DESCRIPTION
11 ssh obtains configuration data from the following sources in the follow-
12 ing order:
13 1. command-line options
14 2. user's configuration file ($HOME/.ssh/config)
15 3. system-wide configuration file (/etc/ssh/ssh_config)
16
17 For each parameter, the first obtained value will be used. The configu-
18 ration files contain sections separated by ``Host'' specifications, and
19 that section is only applied for hosts that match one of the patterns
20 given in the specification. The matched host name is the one given on
21 the command line.
22
23 Since the first obtained value for each parameter is used, more host-spe-
24 cific declarations should be given near the beginning of the file, and
25 general defaults at the end.
26
27 The configuration file has the following format:
28
29 Empty lines and lines starting with `#' are comments.
30
31 Otherwise a line is of the format ``keyword arguments''. Configuration
32 options may be separated by whitespace or optional whitespace and exactly
33 one `='; the latter format is useful to avoid the need to quote whites-
34 pace when specifying configuration options using the ssh, scp and sftp -o
35 option.
36
37 The possible keywords and their meanings are as follows (note that key-
38 words are case-insensitive and arguments are case-sensitive):
39
40 Host Restricts the following declarations (up to the next Host key-
41 word) to be only for those hosts that match one of the patterns
42 given after the keyword. `*' and `?' can be used as wildcards in
43 the patterns. A single `*' as a pattern can be used to provide
44 global defaults for all hosts. The host is the hostname argument
45 given on the command line (i.e., the name is not converted to a
46 canonicalized host name before matching).
47
48 AddressFamily
49 Specifies which address family to use when connecting. Valid ar-
50 guments are ``any'', ``inet'' (use IPv4 only) or ``inet6'' (use
51 IPv6 only).
52
53 BatchMode
54 If set to ``yes'', passphrase/password querying will be disabled.
55 This option is useful in scripts and other batch jobs where no
56 user is present to supply the password. The argument must be
57 ``yes'' or ``no''. The default is ``no''.
58
59 BindAddress
60 Specify the interface to transmit from on machines with multiple
61 interfaces or aliased addresses. Note that this option does not
62 work if UsePrivilegedPort is set to ``yes''.
63
64 ChallengeResponseAuthentication
65 Specifies whether to use challenge response authentication. The
66 argument to this keyword must be ``yes'' or ``no''. The default
67 is ``yes''.
68
69 CheckHostIP
70 If this flag is set to ``yes'', ssh will additionally check the
71 host IP address in the known_hosts file. This allows ssh to de-
72 tect if a host key changed due to DNS spoofing. If the option is
73 set to ``no'', the check will not be executed. The default is
74 ``yes''.
75
76 Cipher Specifies the cipher to use for encrypting the session in proto-
77 col version 1. Currently, ``blowfish'', ``3des'', and ``des''
78 are supported. des is only supported in the ssh client for in-
79 teroperability with legacy protocol 1 implementations that do not
80 support the 3des cipher. Its use is strongly discouraged due to
81 cryptographic weaknesses. The default is ``3des''.
82
83 Ciphers
84 Specifies the ciphers allowed for protocol version 2 in order of
85 preference. Multiple ciphers must be comma-separated. The sup-
86 ported ciphers are ``3des-cbc'', ``aes128-cbc'', ``aes192-cbc'',
87 ``aes256-cbc'', ``aes128-ctr'', ``aes192-ctr'', ``aes256-ctr'',
88 ``arcfour'', ``blowfish-cbc'', and ``cast128-cbc''. The default
89 is
90
91 ``aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour,
92 aes192-cbc,aes256-cbc''
93
94 ClearAllForwardings
95 Specifies that all local, remote and dynamic port forwardings
96 specified in the configuration files or on the command line be
97 cleared. This option is primarily useful when used from the ssh
98 command line to clear port forwardings set in configuration
99 files, and is automatically set by scp(1) and sftp(1). The argu-
100 ment must be ``yes'' or ``no''. The default is ``no''.
101
102 Compression
103 Specifies whether to use compression. The argument must be
104 ``yes'' or ``no''. The default is ``no''.
105
106 CompressionLevel
107 Specifies the compression level to use if compression is enabled.
108 The argument must be an integer from 1 (fast) to 9 (slow, best).
109 The default level is 6, which is good for most applications. The
110 meaning of the values is the same as in gzip(1). Note that this
111 option applies to protocol version 1 only.
112
113 ConnectionAttempts
114 Specifies the number of tries (one per second) to make before ex-
115 iting. The argument must be an integer. This may be useful in
116 scripts if the connection sometimes fails. The default is 1.
117
118 ConnectTimeout
119 Specifies the timeout (in seconds) used when connecting to the
120 ssh server, instead of using the default system TCP timeout.
121 This value is used only when the target is down or really un-
122 reachable, not when it refuses the connection.
123
124 ControlMaster
125 Enables the sharing of multiple sessions over a single network
126 connection. When set to ``yes'' ssh will listen for connections
127 on a control socket specified using the ControlPath argument.
128 Additional sessions can connect to this socket using the same
129 ControlPath with ControlMaster set to ``no'' (the default).
130 These sessions will reuse the master instance's network connec-
131 tion rather than initiating new ones. Setting this to ``ask''
132 will cause ssh to listen for control connections, but require
133 confirmation using the SSH_ASKPASS program before they are ac-
134 cepted (see ssh-add(1) for details).
135
136 ControlPath
137 Specify the path to the control socket used for connection shar-
138 ing. See ControlMaster above.
139
140 DynamicForward
141 Specifies that a TCP/IP port on the local machine be forwarded
142 over the secure channel, and the application protocol is then
143 used to determine where to connect to from the remote machine.
144 The argument must be a port number. Currently the SOCKS4 and
145 SOCKS5 protocols are supported, and ssh will act as a SOCKS serv-
146 er. Multiple forwardings may be specified, and additional for-
147 wardings can be given on the command line. Only the superuser
148 can forward privileged ports.
149
150 EnableSSHKeysign
151 Setting this option to ``yes'' in the global client configuration
152 file /etc/ssh/ssh_config enables the use of the helper program
153 ssh-keysign(8) during HostbasedAuthentication. The argument must
154 be ``yes'' or ``no''. The default is ``no''. This option should
155 be placed in the non-hostspecific section. See ssh-keysign(8)
156 for more information.
157
158 EscapeChar
159 Sets the escape character (default: `~'). The escape character
160 can also be set on the command line. The argument should be a
161 single character, `^' followed by a letter, or ``none'' to dis-
162 able the escape character entirely (making the connection trans-
163 parent for binary data).
164
165 ForwardAgent
166 Specifies whether the connection to the authentication agent (if
167 any) will be forwarded to the remote machine. The argument must
168 be ``yes'' or ``no''. The default is ``no''.
169
170 Agent forwarding should be enabled with caution. Users with the
171 ability to bypass file permissions on the remote host (for the
172 agent's Unix-domain socket) can access the local agent through
173 the forwarded connection. An attacker cannot obtain key material
174 from the agent, however they can perform operations on the keys
175 that enable them to authenticate using the identities loaded into
176 the agent.
177
178 ForwardX11
179 Specifies whether X11 connections will be automatically redirect-
180 ed over the secure channel and DISPLAY set. The argument must be
181 ``yes'' or ``no''. The default is ``no''.
182
183 X11 forwarding should be enabled with caution. Users with the
184 ability to bypass file permissions on the remote host (for the
185 user's X11 authorization database) can access the local X11 dis-
186 play through the forwarded connection. An attacker may then be
187 able to perform activities such as keystroke monitoring if the
188 ForwardX11Trusted option is also enabled.
189
190 ForwardX11Trusted
191 If this option is set to ``yes'' then remote X11 clients will
192 have full access to the original X11 display.
193
194 If this option is set to ``no'' then remote X11 clients will be
195 considered untrusted and prevented from stealing or tampering
196 with data belonging to trusted X11 clients. Furthermore, the
197 xauth(1) token used for the session will be set to expire after
198 20 minutes. Remote clients will be refused access after this
199 time.
200
201 The default is ``no''.
202
203 See the X11 SECURITY extension specification for full details on
204 the restrictions imposed on untrusted clients.
205
206 GatewayPorts
207 Specifies whether remote hosts are allowed to connect to local
208 forwarded ports. By default, ssh binds local port forwardings to
209 the loopback address. This prevents other remote hosts from con-
210 necting to forwarded ports. GatewayPorts can be used to specify
211 that ssh should bind local port forwardings to the wildcard ad-
212 dress, thus allowing remote hosts to connect to forwarded ports.
213 The argument must be ``yes'' or ``no''. The default is ``no''.
214
215 GlobalKnownHostsFile
216 Specifies a file to use for the global host key database instead
217 of /etc/ssh/ssh_known_hosts.
218
219 GSSAPIAuthentication
220 Specifies whether user authentication based on GSSAPI is allowed.
221 The default is ``no''. Note that this option applies to protocol
222 version 2 only.
223
224 GSSAPIDelegateCredentials
225 Forward (delegate) credentials to the server. The default is
226 ``no''. Note that this option applies to protocol version 2 on-
227 ly.
228
229 HashKnownHosts
230 Indicates that ssh should hash host names and addresses when they
231 are added to $HOME/.ssh/known_hosts. These hashed names may be
232 used normally by ssh and sshd, but they do not reveal identifying
233 information should the file's contents be disclosed. The default
234 is ``no''. Note that hashing of names and addresses will not be
235 retrospectively applied to existing known hosts files, but these
236 may be manually hashed using ssh-keygen(1).
237
238 HostbasedAuthentication
239 Specifies whether to try rhosts based authentication with public
240 key authentication. The argument must be ``yes'' or ``no''. The
241 default is ``no''. This option applies to protocol version 2 on-
242 ly and is similar to RhostsRSAAuthentication.
243
244 HostKeyAlgorithms
245 Specifies the protocol version 2 host key algorithms that the
246 client wants to use in order of preference. The default for this
247 option is: ``ssh-rsa,ssh-dss''.
248
249 HostKeyAlias
250 Specifies an alias that should be used instead of the real host
251 name when looking up or saving the host key in the host key
252 database files. This option is useful for tunneling ssh connec-
253 tions or for multiple servers running on a single host.
254
255 HostName
256 Specifies the real host name to log into. This can be used to
257 specify nicknames or abbreviations for hosts. Default is the
258 name given on the command line. Numeric IP addresses are also
259 permitted (both on the command line and in HostName specifica-
260 tions).
261
262 IdentityFile
263 Specifies a file from which the user's RSA or DSA authentication
264 identity is read. The default is $HOME/.ssh/identity for proto-
265 col version 1, and $HOME/.ssh/id_rsa and $HOME/.ssh/id_dsa for
266 protocol version 2. Additionally, any identities represented by
267 the authentication agent will be used for authentication. The
268 file name may use the tilde syntax to refer to a user's home di-
269 rectory. It is possible to have multiple identity files speci-
270 fied in configuration files; all these identities will be tried
271 in sequence.
272
273 IdentitiesOnly
274 Specifies that ssh should only use the authentication identity
275 files configured in the ssh_config files, even if the ssh-agent
276 offers more identities. The argument to this keyword must be
277 ``yes'' or ``no''. This option is intented for situations where
278 ssh-agent offers many different identities. The default is
279 ``no''.
280
281 KbdInteractiveDevices
282 Specifies the list of methods to use in keyboard-interactive au-
283 thentication. Multiple method names must be comma-separated.
284 The default is to use the server specified list.
285
286 LocalForward
287 Specifies that a TCP/IP port on the local machine be forwarded
288 over the secure channel to the specified host and port from the
289 remote machine. The first argument must be a port number, and
290 the second must be [bind_address:]host:port. IPv6 addresses can
291 be specified by enclosing addresses in square brackets or by us-
292 ing an alternative syntax: [bind_address/]host/port. Multiple
293 forwardings may be specified, and additional forwardings can be
294 given on the command line. Only the superuser can forward privi-
295 leged ports. By default, the local port is bound in accordance
296 with the GatewayPorts setting. However, an explicit bind_address
297 may be used to bind the connection to a specific address. The
298 bind_address of ``localhost'' indicates that the listening port
299 be bound for local use only, while an empty address or `*' indi-
300 cates that the port should be available from all interfaces.
301
302 LogLevel
303 Gives the verbosity level that is used when logging messages from
304 ssh. The possible values are: QUIET, FATAL, ERROR, INFO, VER-
305 BOSE, DEBUG, DEBUG1, DEBUG2 and DEBUG3. The default is INFO.
306 DEBUG and DEBUG1 are equivalent. DEBUG2 and DEBUG3 each specify
307 higher levels of verbose output.
308
309 MACs Specifies the MAC (message authentication code) algorithms in or-
310 der of preference. The MAC algorithm is used in protocol version
311 2 for data integrity protection. Multiple algorithms must be
312 comma-separated. The default is ``hmac-md5,hmac-sha1,hmac-
313 ripemd160,hmac-sha1-96,hmac-md5-96''.
314
315 NoHostAuthenticationForLocalhost
316 This option can be used if the home directory is shared across
317 machines. In this case localhost will refer to a different ma-
318 chine on each of the machines and the user will get many warnings
319 about changed host keys. However, this option disables host au-
320 thentication for localhost. The argument to this keyword must be
321 ``yes'' or ``no''. The default is to check the host key for lo-
322 calhost.
323
324 NumberOfPasswordPrompts
325 Specifies the number of password prompts before giving up. The
326 argument to this keyword must be an integer. Default is 3.
327
328 PasswordAuthentication
329 Specifies whether to use password authentication. The argument
330 to this keyword must be ``yes'' or ``no''. The default is
331 ``yes''.
332
333 Port Specifies the port number to connect on the remote host. Default
334 is 22.
335
336 PreferredAuthentications
337 Specifies the order in which the client should try protocol 2 au-
338 thentication methods. This allows a client to prefer one method
339 (e.g. keyboard-interactive) over another method (e.g. password)
340 The default for this option is: ``hostbased,publickey,keyboard-
341 interactive,password''.
342
343 Protocol
344 Specifies the protocol versions ssh should support in order of
345 preference. The possible values are ``1'' and ``2''. Multiple
346 versions must be comma-separated. The default is ``2,1''. This
347 means that ssh tries version 2 and falls back to version 1 if
348 version 2 is not available.
349
350 ProxyCommand
351 Specifies the command to use to connect to the server. The com-
352 mand string extends to the end of the line, and is executed with
353 /bin/sh. In the command string, `%h' will be substituted by the
354 host name to connect and `%p' by the port. The command can be
355 basically anything, and should read from its standard input and
356 write to its standard output. It should eventually connect an
357 sshd(8) server running on some machine, or execute sshd -i some-
358 where. Host key management will be done using the HostName of
359 the host being connected (defaulting to the name typed by the us-
360 er). Setting the command to ``none'' disables this option en-
361 tirely. Note that CheckHostIP is not available for connects with
362 a proxy command.
363
364 PubkeyAuthentication
365 Specifies whether to try public key authentication. The argument
366 to this keyword must be ``yes'' or ``no''. The default is
367 ``yes''. This option applies to protocol version 2 only.
368
369 RemoteForward
370 Specifies that a TCP/IP port on the remote machine be forwarded
371 over the secure channel to the specified host and port from the
372 local machine. The first argument must be a port number, and the
373 second must be [bind_address:]host:port. IPv6 addresses can be
374 specified by enclosing any addresses in square brackets or by us-
375 ing the alternative syntax: [bind_address/]host/port. Multiple
376 forwardings may be specified, and additional forwardings can be
377 given on the command line. Only the superuser can forward privi-
378 leged ports.
379
380 If the bind_address is not specified, the default is to only bind
381 to loopback addresses. If the bind_address is `*' or an empty
382 string, then the forwarding is requested to listen on all inter-
383 faces. Specifying a remote bind_address will only succeed if the
384 server's GatewayPorts option is enabled (see sshd_config(5)).
385
386 RhostsRSAAuthentication
387 Specifies whether to try rhosts based authentication with RSA
388 host authentication. The argument must be ``yes'' or ``no''.
389 The default is ``no''. This option applies to protocol version 1
390 only and requires ssh to be setuid root.
391
392 RSAAuthentication
393 Specifies whether to try RSA authentication. The argument to
394 this keyword must be ``yes'' or ``no''. RSA authentication will
395 only be attempted if the identity file exists, or an authentica-
396 tion agent is running. The default is ``yes''. Note that this
397 option applies to protocol version 1 only.
398
399 SendEnv
400 Specifies what variables from the local environ(7) should be sent
401 to the server. Note that environment passing is only supported
402 for protocol 2, the server must also support it, and the server
403 must be configured to accept these environment variables. Refer
404 to AcceptEnv in sshd_config(5) for how to configure the server.
405 Variables are specified by name, which may contain the wildcard
406 characters `*' and `?'. Multiple environment variables may be
407 separated by whitespace or spread across multiple SendEnv direc-
408 tives. The default is not to send any environment variables.
409
410 ServerAliveInterval
411 Sets a timeout interval in seconds after which if no data has
412 been received from the server, ssh will send a message through
413 the encrypted channel to request a response from the server. The
414 default is 0, indicating that these messages will not be sent to
415 the server. This option applies to protocol version 2 only.
416
417 ServerAliveCountMax
418 Sets the number of server alive messages (see above) which may be
419 sent without ssh receiving any messages back from the server. If
420 this threshold is reached while server alive messages are being
421 sent, ssh will disconnect from the server, terminating the ses-
422 sion. It is important to note that the use of server alive mes-
423 sages is very different from TCPKeepAlive (below). The server
424 alive messages are sent through the encrypted channel and there-
425 fore will not be spoofable. The TCP keepalive option enabled by
426 TCPKeepAlive is spoofable. The server alive mechanism is valu-
427 able when the client or server depend on knowing when a connec-
428 tion has become inactive.
429
430 The default value is 3. If, for example, ServerAliveInterval
431 (above) is set to 15, and ServerAliveCountMax is left at the de-
432 fault, if the server becomes unresponsive ssh will disconnect af-
433 ter approximately 45 seconds.
434
435 SmartcardDevice
436 Specifies which smartcard device to use. The argument to this
437 keyword is the device ssh should use to communicate with a smart-
438 card used for storing the user's private RSA key. By default, no
439 device is specified and smartcard support is not activated.
440
441 StrictHostKeyChecking
442 If this flag is set to ``yes'', ssh will never automatically add
443 host keys to the $HOME/.ssh/known_hosts file, and refuses to con-
444 nect to hosts whose host key has changed. This provides maximum
445 protection against trojan horse attacks, however, can be annoying
446 when the /etc/ssh/ssh_known_hosts file is poorly maintained, or
447 connections to new hosts are frequently made. This option forces
448 the user to manually add all new hosts. If this flag is set to
449 ``no'', ssh will automatically add new host keys to the user
450 known hosts files. If this flag is set to ``ask'', new host keys
451 will be added to the user known host files only after the user
452 has confirmed that is what they really want to do, and ssh will
453 refuse to connect to hosts whose host key has changed. The host
454 keys of known hosts will be verified automatically in all cases.
455 The argument must be ``yes'', ``no'' or ``ask''. The default is
456 ``ask''.
457
458 TCPKeepAlive
459 Specifies whether the system should send TCP keepalive messages
460 to the other side. If they are sent, death of the connection or
461 crash of one of the machines will be properly noticed. However,
462 this means that connections will die if the route is down tem-
463 porarily, and some people find it annoying.
464
465 The default is ``yes'' (to send TCP keepalive messages), and the
466 client will notice if the network goes down or the remote host
467 dies. This is important in scripts, and many users want it too.
468
469 To disable TCP keepalive messages, the value should be set to
470 ``no''.
471
472 UsePrivilegedPort
473 Specifies whether to use a privileged port for outgoing connec-
474 tions. The argument must be ``yes'' or ``no''. The default is
475 ``no''. If set to ``yes'' ssh must be setuid root. Note that
476 this option must be set to ``yes'' for RhostsRSAAuthentication
477 with older servers.
478
479 User Specifies the user to log in as. This can be useful when a dif-
480 ferent user name is used on different machines. This saves the
481 trouble of having to remember to give the user name on the com-
482 mand line.
483
484 UserKnownHostsFile
485 Specifies a file to use for the user host key database instead of
486 $HOME/.ssh/known_hosts.
487
488 VerifyHostKeyDNS
489 Specifies whether to verify the remote key using DNS and SSHFP
490 resource records. If this option is set to ``yes'', the client
491 will implicitly trust keys that match a secure fingerprint from
492 DNS. Insecure fingerprints will be handled as if this option was
493 set to ``ask''. If this option is set to ``ask'', information on
494 fingerprint match will be displayed, but the user will still need
495 to confirm new host keys according to the StrictHostKeyChecking
496 option. The argument must be ``yes'', ``no'' or ``ask''. The
497 default is ``no''. Note that this option applies to protocol
498 version 2 only.
499
500 XAuthLocation
501 Specifies the full pathname of the xauth(1) program. The default
502 is /usr/X11R6/bin/xauth.
503
504FILES
505 $HOME/.ssh/config
506 This is the per-user configuration file. The format of this file
507 is described above. This file is used by the ssh client. Be-
508 cause of the potential for abuse, this file must have strict per-
509 missions: read/write for the user, and not accessible by others.
510
511 /etc/ssh/ssh_config
512 Systemwide configuration file. This file provides defaults for
513 those values that are not specified in the user's configuration
514 file, and for those users who do not have a configuration file.
515 This file must be world-readable.
516
517SEE ALSO
518 ssh(1)
519
520AUTHORS
521 OpenSSH is a derivative of the original and free ssh 1.2.12 release by
522 Tatu Ylonen. Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, Theo
523 de Raadt and Dug Song removed many bugs, re-added newer features and cre-
524 ated OpenSSH. Markus Friedl contributed the support for SSH protocol
525 versions 1.5 and 2.0.
526
527OpenBSD 3.6 September 25, 1999 8